Catheter-based devices for use in surgical procedures and other medical applications are known. One category of such devices is the minimally-invasive, catheter-based device that is introduced into the vasculature. Low temperature fluid, or cryogens, may be used with such catheters to cold-treat target areas. Such devices use cold to treat selected body tissues through the energy transfer derived from thermodynamic changes occurring in the flow of a cryogen through the device. This energy transfer creates a net transfer of heat from the target tissue to the device, typically achieved by cooling a portion of the device to very low temperature through conductive and convective heat transfer between the cryogen and target tissue.
Structurally, the cryogenic fluid is injected into an expansion chamber through an orifice in an injection tube that supplies the fluid. Upon injection into the expansion chamber, the cryogen undergoes two primary thermodynamic changes: (i) expanding to low pressure and temperature through positive Joule-Thomson throttling, and (ii) undergoing a phase change from liquid to vapor, thereby absorbing heat of vaporization. The resultant flow of low temperature cryogen through the expansion chamber acts to absorb heat from the target tissue and thereby cool the tissue to the desired temperature.
In order to cool a treatment segment at a distal end of a device having an expanded or larger surface area than the device body, for example, effective cooling may be achieved by either uniformly spraying or dispersing refrigerant onto the expanded surface of the treatment segment, or by flooding the treatment segment with a refrigerant. Flooding a treatment segment may require larger volumes of coolant, resulting in inefficient use and increased costs. When flooding a treatment segment, the phase change of the cryogen is not controlled and may not occur at the location where the catheter contacts the tissue which is intended to be ablated. As well, the cryogen may return from the balloon as a cold liquid that will cool the catheter shaft, potentially ablating adjacent tissue unintentionally. These shortcomings make the substantially uniform spraying or dispersion of coolant an attractive alternative. Devices as depicted in U.S. Pat. No. 6,235,019 provide multiple coolant injection tubes. Alternatively, as shown in U.S. Pat. No. 5,899,898, a single injection tube can be provided with openings along its length.
However, the dispersion of coolant from these devices is performed in a fixed direction, i.e., the orifice or ports from which the coolant is sprayed disperse the coolant in a non-varying direction. It is therefore desirable to provide a device which optimizes the cooling power of the flow of cryogenic fluid therethrough, namely through controllably directing a supply of high pressure cryogen to a target tissue and thereby increase the cooling efficiency.